Arthur Ashe Stadium sits empty as rain falls on the court at the 2014 U.S. Open tennis tournament in New York, August 31, 2014.Ray Stubblebine

NEW YORK (Reuters) - Severe thunderstorms on Sunday forced an early end to New York's Electric Zoo music festival, delayed flights at area airports and injured two people after a lightning strike near a Bronx beach.

Rain halted play at the U.S. Open in Queens, New York, interrupted the Made In America outdoor concert in Philadelphia and shut down the Electric Zoo electronic music festival on Randalls Island in New York, which ended early for a second year in a row.

"We apologize to fans, but your safety is our main concern," Electric Zoo organizers said in a Tweet explaining why the three-day festival was cut short by "extreme weather." Thousands of concertgoers were told to leave.

The festival ended early last year due to the deaths of two concertgoers who used an illicit drug known as Molly, and the tragedy led to new safety protocols this year.

Severe weather quickly swept across the metropolitan area in the late afternoon, with lightning striking a tree near Orchard Beach in the Bronx, injuring two people who were standing beneath it, said National Weather Service meteorologist Lauren Nash. They were taken to Jacobi Medical Center but a hospital spokeswoman declined to comment on their conditions.

Torrential rain and strong winds caused widespread delays at all airports in the New York metropolitan area as well as Philadelphia International Airport, according to FlightAware.com.

Skies cleared quickly after the early evening storm, although there were some lingering rain clouds.

"We could still see some showers or thunderstorms overnight in the New York area," meteorologist Nash said.